Wireless and retrofittable in-shoe system for real-time estimation of kinematic and kinetic gait parameters

ABSTRACT

A quantitative gait training and/or analysis system includes one or more footwear modules that may include a piezoresistive sensor, an inertial sensor and an independent logic unit. The footwear module functions to permit the extraction of gait kinematics and evaluation thereof in real time, or data may be stored for later reduction and analysis. Embodiments relating to calibration-based estimation of kinematic gait parameters are described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/457,730, filed Jun. 28, 2019, which claims priority to U.S.Provisional Patent Application Ser. No. 62/692,568 filed Jun. 29, 2018,the disclosures of which are incorporated herein by reference in theirentireties, including Exhibits A-C attached thereto.

FIELD OF THE INVENTION

The present disclosure relates generally to systems, methods, anddevices for gait analysis and training, and, more particularly, to awearable, autonomous apparatus for quantitative analysis of a subject'sgait and/or providing feedback for gait training of the subject.Particular applications of interest arise in sport performanceassessment and elderly care.

BACKGROUND OF THE INVENTION

Pathological gait (e.g., Parkinsonian gait) is clinically characterizedusing physician observation and camera-based motion-capture systems.Camera-based gait analysis may provide a quantitative picture of gaitdisorders. However, camera-based motion capture systems are expensiveand are not available at many clinics. Auditory and tactile cueing(e.g., metronome beats and tapping of different parts of the body) areoften used by physiotherapists to regulate patients' gait and posture.However, this approach requires the practitioner to closely follow thepatient and does not allow patients to exercise on their own, outsidethe laboratory setting.

Compared to traditional laboratory equipment for gait analysis,instrumented footwear systems are more affordable and versatile. Thesedevices can be used to assess the wearers' gait in unrestrictedenvironments, in diverse motor tasks, and over extended time periods.

Quantitative gait analysis is a powerful diagnostic tool for physicianstreating patients with gait disorders. Athletic trainers often rely onassessments of the running gait when coaching professional athletes whoare recovering from an injury or want to improve their performance.Quantitative gait analysis requires specialized laboratory equipmentsuch as optical motion capture systems and treadmills instrumented withforce plates or other force mapping systems. For this reason, the use ofgait analysis is currently limited by high operating costs and lack ofportability.

In recent years, several instrumented footwear systems have beendeveloped for portable gait assessments. Compared to traditionallaboratory equipment, these new systems are more affordable andversatile. However, the amount of parameters these devices can assess isstill limited, and their accuracy is usually poor and not comparable tothat of standard laboratory equipment.

OBJECTS OF THE INVENTION

Certain prior art devices are incapable of estimating the user's centerof mass (COM) and dynamic margin of stability (MOS). It is therefore anobject of the present invention to quantify the position of the COM, theMOS and other indices of dynamic stability. This object is met by thepresent invention's use of insoles instrumented with inertial,piezoresistive and time-of-flight proximity sensors.

It is another object of the present invention to measure thecoordination between upper and lower extremities, as well as to measurea broad set of kinematic and kinetic gait parameters, including, forexample, inter-limb parameters such as double support time.

Yet another object of the present invention is to provide wirelessfunctionality and to be lightweight (i.e., below 100 grams) andaffordable (i.e., $500 or less), while simultaneously featuring a highsampling rate (500 Hz), making it superior for highly dynamic tasks.

Another object of the present invention is to provide a broad set ofinformation, including plantar pressure maps and center-of-pressure(CoP) trajectories, that can be used for both performance tracking andinjury prevention.

Yet another object of the present invention is to make it possible tocreate remotely-monitored, self-administered walking and balanceexercises for the elderly which can potentially increase safety andrelieve the financial burden on the healthcare system.

Another object is to provide a completely wireless and portableinterface that allows the wearer's own shoes to be retrofitted with thepresent invention, thereby eliminating the need to modify the shoesthemselves.

Yet another object of the invention is to circumvent conventionallimitations of portable gait-monitoring systems by presenting novelcalibration algorithms based on machine learning and biomechanicalmodels of human locomotion.

A further object of the invention is to enable sport performanceevaluation (e.g., running technique) and clinical gait assessments inpatients with movement disorders.

Additional objects of the invention include: providing fall riskassessment and fall detection in the elderly, aiding injury preventionin athletes and in the elderly, offering gait or balance rehabilitationwith real-time augmented feedback, generating monitoring or activityclassification for vulnerable older adults, and aiding pedestriannavigation.

SUMMARY

The present invention is an improvement over and/or a supplement to thesystems, devices and methods disclosed U.S. Patent ApplicationPublication No. 2017/0055880, the contents of which are incorporated byreference herein. More particularly, the device of the present inventionmeasures a broad set of spatio-temporal gait parameters (e.g., stridelength, foot-ground clearance, foot trajectory, cadence, single anddouble support times, symmetry ratios and walking speed), as well askinetic parameters (i.e., dynamic plantar pressure maps, CoPtrajectories) during different tasks (e.g., walking and running tasks).By applying custom calibration algorithms (see, for example, FIGS. 1 and2 , which are referenced and described in greater detail hereinbelow) tothe raw data measured by the embedded sensors, the device can assess allgait parameters within 1-2% accuracy. This feature allows the presentinvention to capture subtle changes in gait parameters that are knownprecursors of injuries or imbalance, and to precisely assess anathlete's running technique.

A system assembled in accordance with the present invention utilizesaffordable, mid-level sensors, while providing the option of auditoryand vibro-tactile feedback that can be utilized by a user for gaitrehabilitation. Another application for the data collected by the systemis activity monitoring/classification. This can be realized with machinelearning models to automatically classify activities of daily livingbased on the signals recorded by the system. Additionally, the systemcan potentially be used with a smartphone equipped with GPS to realize aportable navigation system. Higher accuracy for the system is achievedthrough the calibration algorithms referenced above and described ingreater detail in attached FIGS. 1 and 2 . Higher accuracy makes itpossible to detect subtle changes in the user's gait, which can beprecursors of imbalance or injuries.

Most existing portable devices cannot simultaneously estimate temporalparameters, spatial parameters, and kinetic parameters. Although a fewsuch devices may be able to achieve this goal, they suffer from alimited sample rate, which makes them unsuitable for assessments ofhighly dynamic tasks. Additionally, these devices cannot estimate someimportant gait parameters, such as foot-ground clearance, foottrajectory, single and double support times, symmetry ratios, CoPtrajectories, etc., making them unsuitable for clinical gaitassessments.

Traditional gait analysis systems for clinical assessments and sportperformance assessments require expensive laboratory equipment,including force plates and optical motion capture systems. Portable gaitanalysis systems have the advantage of being lightweight andcost-effective, and are not constrained to the laboratory environment,thus making it possible to assess gait metrics in daily-life scenarios.This has important implications for clinical diagnostics, activitymonitoring, as well as performance evaluation in sports.

BRIEF DESCRIPTION OF FIGURES

For a more complete understanding of the present disclosure, referenceis made to the following drawings, in which:

FIG. 1 is a schematic illustration of the first step of a novel two-stepcalibration approach for the CoP, illustrating a static calibrationframework for multi-cell pressure insoles; and

FIG. 2 is a schematic illustration of the second step of a noveltwo-step calibration approach for the CoP, illustrating a dynamiccalibration framework for CoP trajectories.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In an embodiment, the present invention is a device comprising twoinsole modules and a data logger. Each insole module is wireless, havinga transmission unit, as well as the ability to accurately measurekinematic and kinetic gait parameters of a user in a variety of dynamictasks (e.g., walking, running, negotiating stairs, etc.), both outdoorand indoor. In an embodiment, all the data are collected at 500 Hz andsent wirelessly to a battery-powered single-board computer (or mobiledevice) running a data-logger. In an embodiment, the single-boardcomputer fits inside a running belt that can be worn by the user or canbe optionally located offboard within a 30-meter range from the user.

In an embodiment, each insole module consists of an eight-cellpiezoresistive sensor, a nine degree-of-freedom inertial sensor, and acustom-made logic unit. The pressure sensors are located, for instance,underneath the calcaneous, the lateral arch, the head of the first,third and fifth metatarsals, the hallux, and the toes, while theinertial sensor is placed, for instance, along the midline of the foot.

In an embodiment, the logic unit includes a microcontroller interfacedwith the multi-cell pressure sensor through an eight-channelmultiplexer, while communicating with the inertial sensor through aserial connection. In an embodiment, all the data are sampled at 500 Hzand sent through UDP over WLAN to the single-board computer by means ofa Wi-Fi module. The logic unit, which can be housed in a plasticenclosure, is powered by, for instance, a small 400 mAh Li-po batterythrough a step-up voltage regulator.

In an embodiment, the single-board computer runs a Linux distributionwith a real-time kernel operating in headless mode. A miniature Wi-Firouter can be connected to the computer, serving as an access point. Inuse, for example, the computer synchronizes the data incoming from theinsole modules and writes them to a micro-SD card. The same data canalso be streamed at a lower sample rate (50 Hz) to an easy-to-use userinterface running on the user's laptop or mobile phone, whereby theinterface allows the user to control the device remotely and tovisualize measured data.

Other features, attributes and exemplary embodiments of the presentinvention are disclosed and illustrated in the publication by HuangheZhang et al., titled “Estimating CoP Trajectories and Kinematic GaitParameters in Walking and Running Using Instrumented Insoles,” IEEERobotics and Automation Letters, Vol. 2, No. 4, Oct. 2017, pp.2159-2165, and in the publication by Huanghe Zhang et al., titled“Regression Models for Estimating Kinematic Gait Parameters withInstrumented Footwear,” IEEE International Conference on BiomedicalRobotics and Biomechatronics, Aug. 2018,both publications beingincorporated by reference herein in their entireties and thereforeconstituting part of the present application. In addition to theincorporation by reference immediately above, it is noted that theformer publication identified above was attached as

Exhibit B in the related provisional U.S. patent application referencedabove and incorporated by reference herein. With regard to the latterpublication identified above, an earlier, unpublished version wasattached as Exhibit C to the aforementioned provisional U.S. patentapplication.

It will be understood that the embodiments described in the foregoingspecification and claims, as well those described in the variousdocuments incorporated by reference herein, are merely exemplary andthat a person skilled in the art may make many variations andmodifications without departing from the spirit and scope of the presentinvention.

We claim:
 1. A gait measurement system, comprising: at least one insolemodule for placement in a shoe of a user, each of said at least oneinsole module including a piezoresistive sensor, an inertial sensor, alogic unit communicatively coupled to said piezoresistive sensor and tosaid inertial sensor, and a transmission unit; and a computing unitcommunicatively coupled to said inertial sensor and said piezoresistivesensor via said transmission unit.
 2. The gait measurement system ofclaim 1, wherein said piezoresistive sensor includes a plurality ofpressure-sensing cells.
 3. The gait measurement system of claim 2,wherein said plurality of pressure-sensing cells includes eight of saidcells.
 4. The gait measurement system of claim 2, wherein at least someof said plurality of pressure-sensing cells are located beneath a user'scalcaneous, a user's lateral arch, a head of a user's first metatarsal,a head of a user's third metatarsal, a head of a user's fifthmetatarsal, a user's hallux and a user's toes.
 5. The gait measurementsystem of claim 1, wherein each of said at least one insole module isadapted to be retrofitted to a shoe of a user.
 6. The gait measurementsystem of claim 1, wherein said inertial sensor has nine-degrees offreedom.
 7. The gait measurement system of claim 1, wherein saidinertial sensor is located along a portion of said at least one insolemodule corresponding to a midline of a user's foot.
 8. The gaitmeasurement system of claim 1, wherein each of said at least one insolemodule further comprises feedback means for providing vibro-tactilefeedback to a user.
 9. The gait measurement system of claim 1, whereinsaid logic unit is configured to sample data at 500 Hertz.
 10. The gaitmeasurement system of claim 1, wherein said system is configured toestimate center of pressure and/or dynamic margin of stability.
 11. Thegait measurement system of claim 1, wherein said system is adapted tomeasure inter-limb parameters.
 12. The gait measurement system of claim1, wherein said system is adapted to measure one or more gait parametersselected from the group consisting of stride length, foot-groundclearance, foot trajectory, cadence, double support time, single supporttime, walking speed, center of pressure, and margin of stability. 13.The gait measurement system of claim 12, wherein said computing unit isfurther adapted to generate dynamic plantar pressure maps and/or centerof pressure trajectories.
 14. The gait measurement system of claim 1,wherein said computing unit is adapted to classify activities of dailyliving.
 15. The gait measurement system of claim 1, wherein said systemis adapted to cooperate with a mobile device having GPS in order torealize a portable navigation system.
 16. The gait measurement system ofclaim 1, wherein said system is adapted to remotely monitor andadminister walking and/or balance exercises.
 17. The gait measurementsystem of claim 1, wherein said system is adapted to provide gait and/orbalance rehabilitation.
 18. A method for calibrating a gait measurementsystem, comprising the steps of: i) providing an instrumented insolehaving a plurality of pressure-sensing cells; ii) exerting known,uniform pressure on said instrumented insole; iii) recording arespective output for each of said pressure-sensing cells in response topressure exerted on said instrumented insole during the performance ofstep (ii); iv) applying a plurality of fitting functions to saidrespective output of each of said pressure-sensing cells, therebyobtaining a plurality of respective model data; and v) applying crossvalidation to said respective model data to obtain a calibration modelfor each of said pressure-sensing cells.
 19. A method for calibrating agait measurement system, comprising the steps of: i) providing aninstrumented insole and a reference measuring apparatus; ii) recording afirst data set from said instrumented insole and a second data set fromsaid reference measuring apparatus; iii) computing center of pressuretrajectories from said first and said second data sets; iv) validatingthe accuracy of said center of pressure trajectories using one or moreregression models; and v) calibrating said instrumented insole via saidfirst and said second data sets.